This invention relates to a rotor assembly for an electric motor or the like, and more particularly to a die cast, squirrel cage rotor having a tubular oil return member sealingly cast-in-place within the rotor.
In certain dynamoelectric machines of the inductive motor type, and particularly in many smaller motors sometimes referred to as unit bearing motors, the motors have a squirrel cage rotor assembly in which the conductor bars for the rotor and the body of the rotor are made of die cast aluminum. Typically, these rotor assemblies include a stack of individual laminations constructed from suitable magnetic material. Each lamination has a central opening and a plurality of so-called satellite openings adjacent their outer margins. The laminations are assembled in a stack and the laminations are rotated slightly with respect to one another in the stack so that their central openings are coaxial but so that their satellite openings are skewed relative to one another and so that the satellite openings constitute slots. The lamination stack is then placed in a suitable die casting mold and molten aluminum is injected under pressure into the mold so as to surround the lamination stack, to fill the mold, and to flow through the skewed slots in the lamination stack formed by the satellite openings so as to form the conductor bars of the rotor. These die cast squirrel cage rotors typically have a central opening therethrough and a rotor shaft extending through this opening which is rigidly secured to the rotor so that the shaft rotates with the motor. This central opening may be defined at least in part by the central opening of the laminations and is appreciably larger than the shaft so as to receive a rigid boss of the motor housing. The rotor shaft is received in an opening in the boss and is journalled therein by a suitable journal bearing or the like so as to rotatably support the rotor on the motor housing. As is typical, a portion of the rotor shaft journalled in the bearing has a helical oil groove formed on its outer surface and the outer end of the shaft rotates in a felt wick supplied with lubricating oil from a reservoir. Upon rotation of the rotor, the oil grooves in the shaft pick up oil from the wick and move it along the length of the bearing to lubricate it. Upon the oil being discharged from the inner end of the bearing, it is slung outwardly by the centrifugal force of the rotating rotor shaft.
In prior art motors having such rotors, a return system was provided for recirculating the oil back to the oil supply reservoir. This oil return system typically included a tubular oil return member which was fitted into the opening in the rotor after die casting. This oil return member surrounded the bearing boss and extended out beyond the end of the rotor. The inner end of this oil return member was sealed to the rotor body by application of a sealant. An outer end cap carried by the motor housing surrounded the outer end of the oil return member and collected oil which flowed out the end of the oil return member from the inside of the rotor.
In the manufacture of these prior die cast squirrel cage rotors, it has heretofore been difficult to fit the oil return member into the rotor body and to seal the inner end of the oil return member to the rotor body. As mentioned above, the sealing operation usually involved the application of a sealant to the joint between the inner end of the oil return member and the rotor body. However, many of the motors which incorporated these die cast squirrel cage rotors were relatively small and the space in which the sealant had to be applied was cramped. Also, the application of sealant was a messy and time consuming operation performed after die casting of the rotor thus resulting in increased labor costs for the manufacture of the motor.